Chef config used mixlin config under the hood , you should be able to
assign any value directly,

Chef::Config[:file_cache_path]= ‘foo’

Also this is chef client related configuration, hence it might vary
depending upon chef version (hosted chef, opensource chef , private chef …
chef server in general does not control this). All this configs are defined
in lib/chef/config.rb , and you can specify this in your client.rb file as
well, like
file_cache_path = ‘/var/chef/cache’ (currently this is the default btw)